Many industrial plants store large quantities of chemical compounds which are used in processing operations or are produced by such processing operations. Many of these compounds, if released into the atmosphere, could prove quite hazardous to people and the environment. As many industrial plants are located near population centers, the risk of injury to the people from such a release is great. It is imperative, then, that efforts be taken to prevent the release of these compounds or, if released, to prevent the spread of the compound to the populated area.
Depending on the type of chemical compound, a release--as for example from a ruptured line or tank--may be in the form of a liquid spill or a gas or vapor release. Liquid spills are more easily contained through the use of dams, dikes, liquid brooms and the like. The pooled liquid material may, however, continue to provide a significant source of vapors as the pooled material evaporates.
A sudden or sustained release of a material stored at a pressure or temperature other than ambient temperature and pressure may produce a significant fraction of the released material as vapor and/or aerosol, due to the change in enthalpy of the stored versus released material. A release in the form of a gas or vapor poses a greater difficulty. The gas or vapor can originate directly from a ruptured line or vessel of the processing or storage equipment, or it may originate from surface vaporization of a pool of collected liquid or due to a change from storage to ambient temperature or pressure. If the gas or vapor is lighter than air, as for example a fluorocarbon, it will rise from its source to be disposed in the upper regions of the atmosphere, thereby creating little risk to the local environment. However, if the vapor or gas is neutrally buoyant or heavier than air, or cryogenic or transiently polymeric--as for example hydrogen fluoride--, it will tend to form a contaminant cloud which will remain near ground level.
These contaminant clouds may be influenced by local terrain as well as prevailing meteorological conditions. Particularly dense contaminant clouds may be long-lasting, slow to entrain air, and may present hazardous concentrations over long distances. Some materials which, if released into the environment, may form hazardous contaminant clouds include ammonia, acrylonitrile, hydrogen cyanide, hydrogen fluoride, hydrogen sulfide, alkylation acid, chlorine, tetraethyl lead and hydrocarbons, to name but a few.
Current practices to control, diffuse or neutralize contaminant clouds are ineffective in most instances. One practice involves the erection of physical, impermeable barriers. The barriers may be in the form of walls made of suitable plastic material which provide some retardation of the leading edge of the contaminant cloud. However, once the contained area fills with the contaminant material, the cloud will flow over the top, creating yet another hazardous release.
Furthermore, such physical barriers are unsafe, indeed dangerous, in the event of a release of a hydrocarbon. The turbulence caused when a highly concentrated hydrocarbon cloud strikes the physical barrier may set off an unconstrained vapor cloud explosion. Such explosions have reached forces of 10 kilotons. Accordingly, when physical barriers are employed around a facility wherein a hydrocarbon is one of several stored chemical compounds, it must be possible to establish and remove the barrier quickly in the event of a hydrocarbon release.
Other practices to control or mitigate the contaminant cloud include water or chemical sprays. Water sprays may serve temporarily to reduce the cloud concentration but create a contaminated aqueous solution which itself must be controlled, and which may re-vaporize, creating a new release source. Chemical sprays may react with the cloud, altering its chemical composition or physical state and rendering it non-hazardous. Such sprays, however, may react with a limited amount of the contaminant cloud, leaving the remainder to continue posing an environmental hazard.
If the contaminant cloud originates from a pool of contaminant, a foam or cover may be applied over the surface of the pool to reduce vaporization. Such measures are effective only for pools and then only for some liquid contaminants.
Yet another practice to mitigate the effects of contaminant clouds is to apply heat, in the form of flares or steam sprays. The heated cloud may become less dense, to the point of being buoyant, thereby rising into the atmosphere and away from the local environment. In addition, the flare may burn the contaminant thereby chemically altering it into a manageable form, such as a precipitate or non-hazardous gas. The use of steam sprays or flares, however, generally have less than desirable results. The heated cloud may rise temporarily but later may again become denser as it cools, returning to ground level in a continued hazardous concentration. Additionally, some contaminants are explosive in concentrated form, thus making the use of flares and open flames extremely dangerous.
Despite the wide use of chemical compounds in industrial operations and the great potential for environmental releases of such compounds, and further despite the hazards such releases may pose for the local environment, no effective practice has previously been developed to control, dissipate, neutralize or otherwise mitigate the effect of the contaminant clouds formed by such release. The known practices for countering environmental releases of contaminants are limited to the types of contaminants for which they may be used; and, even when usable, these practices are moderately effective, at best.